This invention relates to a threading apparatus on a sewing machine for facilitating of the threading of a needle.
Such threading apparatus is proposed, for example, in Japan Published Unexamined Patent Application No. H1-113092, in which a spring raises an actuating rod and an air cylinder lowers the actuating rod. When the actuating rod lowers, a threading rod lowers and further rotates, a threading hook enters a needle eye, and thread is caught in the threading hook. The threading hook leaves the needle eye, thereby drawing one end of the thread into and through the needle eye.
However, in the related-art threading apparatus the actuating rod is connected to the air cylinder through string members. If the air cylinder fails to operate because of the breakage of the air cylinder or an incorrect supply of air to the air cylinder, the actuating rod also fails to operate. The actuating rod can be lowered only by means of the air cylinder. Therefore, when the air cylinder breaks, a needle cannot be threaded with the threading hook.
The threading apparatus should be assembled by placing the threading hook and the needle eye in a predetermined relative position so that the threading hook can be inserted through the needle eye. For example, when the needle is in the predetermined position, the threading rod lowered by the actuating rod is prevented through a positioning stop member or the like from lowering further, and the threading hook is aligned with the needle eye. The actuating rod further lowers, the threading rod rotates, and the threading hook goes through the needle eye. When the threading apparatus is assembled, the position of the positioning stop member is adjusted so that the threading hook can be aligned with the needle eye. The threading hook is aligned with the needle eye by vertically moving the threading hook. For such adjustment, the air cylinder is driven. Alternatively, the air cylinder is disconnected from the actuating rod, the threading rod is manually moved to align the threading hook with the needle eye, and the air cylinder is again connected to the actuating rod. The position adjustment is a time-consuming operation.